The present invention is directed to an igniter nozzle for gas turbines and, more particularly, to a combination igniter and fuel atomizer nozzle assembly for the start up of gas turbines.
A wide variety of fuel atomizer and igniter arrangements have been employed in the past for the ignition of fuel for the start up of gas turbines. In one such arrangement the fuel is admitted to the turbine combustion chamber through atomizers which are used to deliver fuel throughout the operating range of the turbine engine. This fuel is atomized and is directed toward a conventional igniter. The igniter typically comprises an electrode which is surrounded by an insulator, and by an electrically conductive housing which surrounds the insulator. The ends of the electrode and of the housing open into the combustion chamber where fuel is atomized during normal turbine operation, and the housing extends through the air plenum of the turbine to the gas generator case, to utilize air cooling effects. In this arrangement the igniter is spaced from the normal-operation fuel atomizer in the combustion chamber. The atomized fuel is directed toward the igniter, and when electrical energy is imparted to the electrode, a spark jumps from the electrode to the housing to ignite the fuel proximate the end of the igniter. The flame produced at the igniter upon ignition is then propagated as a flame front back to the main-operation fuel atomizer to ignite the fuel as it issues from the main-operation atomizer.
One disadvantage of this arrangement is that movement of discharge air, used for cooling the igniter, tends to blow atomized fuel droplets away from the end of the igniter, extending the time required for ignition and substantially increasing the amount of start-up smoke generation. This slow ignition is also disadvantageous particularly in aircraft engines where it is desired to restart a flameout at high altitudes at which the start up is further hampered by cold fuel and relatively high air velocities. Moreover, in this arrangement relatively high electrical energies are required due to the spacing of the atomizer and igniter in the combustion chamber. High electrical energies substantially decrease the life of the igniter.
Another arrangement has also been employed in the past in which the igniter is incorporated into the fuel atomizer housing. However, this arrangement results in a large, cumbersome and heavy atomizer housing, and as a result, its use is essentially limited to land operating turbines. Moreover, this arrangement, because it is incorporated into the normal main-operation atomizer housings, subjects the igniter to continuous exposure to the flame even after start up is achieved, which reduces the life of the igniter and subjects the igniter to carbon buildup.
In the igniter and fuel atomizer nozzle assembly and method of the present invention a fuel atomizer nozzle is incorporated directly into the igniter housing, and the start up fuel is atomized closely proximate the spark which is generated by the igniter. Once combustion has been initiated in the combustion chamber, the start up fuel flow to the atomizer in the igniter may be terminated, and the atomizer can be purged to minimize further carbon buildup. Once ignition has occurred, the normal operation of the turbine is accomplished by way of the normal main-operation fuel atomizers.
The assembly and method of the present invention thereby overcomes most if not all of the aforementioned disadvantages of the aforementioned prior start up arrangements. In the present invention the atomized fuel for start up and the igniter spark are positioned in extremely close proximity to each other which results in substantially improved ignition. This configuration results in faster ignition and simplifies the main fuel system because there is no longer any need to incorporate start up capabilities in the main fuel nozzle which is designed for normal operation versus start up. The faster ignition also substantially reduces start up smoking and improves the ignition under high altitude start up conditions when the fuel is cold and the air velocity is high. The extremely close proximity of the start up atomized fuel and the spark may also reduce the electrical energy requirements of the igniter and, therefore, substantially increases the life of the igniter. Because the start up atomizer in the igniter is only needed for start up and can be purged of its fuel after ignition, carbon buildup on the igniter may also be substantially reduced. The assembly of the present invention is capable of achieving these substantial advantages with at most only a minimum reconfiguration of a standard igniter assembly, and because it is extremely compact it may be readily utilized in aircraft turbines and not just land use turbines.
In one principal aspect of the present invention, a combination igniter and fuel atomizer nozzle assembly comprises an igniter which includes an elongate conductive electrode and an elongate conductive housing surrounding the electrode so as to define an elongate passageway in the housing between the electrode and the housing. The ends of the electrode and the housing are positioned proximate to each other to define a gap through which a spark will jump between the ends of the housing and the electrode when electrical energy is imparted to either the electrode or the housing. A fuel atomizer nozzle includes a fuel discharge orifice proximate the ends of the electrode and the housing and adjacent to the gap for the purpose of discharging finely atomized fuel adjacent the gap. Also, a fuel conduit is in the passageway for communicating fuel to the orifice for discharge therefrom.
In another principal aspect of the present invention, the orifice is in the passageway of the igniter housing.
In still another principal aspect of the present invention, the atomizer nozzle is a simplex nozzle.
In still another principal aspect of the present invention, an electrically insulative material is in said passageway and surrounds the electrode and is between the electrode and the conduit and housing.
In still another principal aspect of the present invention, the fuel discharge orifice is between the aforementioned insulative material and the housing.
In still another principal aspect of the present invention, the end of the housing includes a cap, and the cap has an opening therein through which the end of the electrode is exposed. The perimeter of the opening is spaced from the end of the electrode to at least in part define the gap, and the orifice is between the elongate housing and the perimeter of the opening.
In still another principal aspect of the present invention, one or more second openings are located in the cap between the perimeter of the opening through which the electrode is exposed and the elongate housing, and the orifice discharges the finely atomized fuel through at least one of these second openings.
In still another principal aspect of the present invention, a method of initiating combustion start up in a gas turbine engine comprises passing combustible fuel through the elongate housing of an igniter, atomizing the fuel adjacent the end of the igniter which is positioned in the combustion chamber of the gas turbine engine, discharging the atomized fuel from the end of the igniter housing and into the combustion chamber, and imparting electrical energy to an electrode in the igniter housing to initiate an electrical spark at the end of the electrode and igniter housing and closely proximate the location from which the atomized fuel is discharged from the end of the igniter housing to ignite the atomized fuel.
In still another principal aspect of the present invention, the fuel is atomized before it is discharged from the end of the igniter housing.
In still another principal aspect of the present invention, the location at which the fuel is initially atomized is proximate to but spaced from the path of the spark.
In still another principal aspect of the present invention, the fuel remaining in the atomizer housing is purged once ignition of the fuel has been initiated.
In still another principal aspect of the present invention, air is passed through the igniter housing and is discharged from the end of the housing.
These and other objects, features and advantages of the present invention will be more clearly understood upon consideration of the detailed description of the preferred embodiment of the invention which will be described to follow.